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10.3 Stationary waves in 10.3 Stationary waves in airair

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10.3 Stationary waves in air (SB p. 141)

Stationary waves in air

Stationary waves in air obtained by:

sound wave from loudspeaker is

reflected

superposition of waves

dffv

xxd

2air in sound of Speed2

antinodes successive 2between Distance 12

v = 2fdGo to

Example 6Example 6

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End

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Q:Q: S1 and S2 are two loudspeakers which emit sound waves of frequency 1 100 Hz continuously. M is a small microphone which is moved along the line joining S1 and S2 with a speed of 30 m s–1.

(a) The sound received by M rises and falls periodically. Explain why.(b) If the speed of sound is 330 m s–1, calculate the frequency of the rise and fall in the sound received by M. Solution

10.3 Stationary waves in air (SB p. 142)

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Solution:Solution:

Hz 2000.1530

microphone by the received sound in the fall and rise ofFrequency

m 1502

antinodes successive obetween tw Distance

m 3001100330 Wavelength

.

.fv

10.3 Stationary waves in air (SB p. 142)

(a) Sound waves from S1 and S2 are of the same frequency and amplitude but travelling in opposite directions. The superposition of the waves produces a stationary wave between S1 and S2 . At the antinodes of the stationary wave, the vibration is of large amplitude and a loud sound is detected by the microphone. At the nodes, the amplitude is zero and no sound is detected.(b) Frequency, f = 1 100 Hz, speed of sound v = 330 m s–1

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